Insulated electric cable



oct. 19, 1937.v P, M, CLARK 2,096,448

INSULATED ELECTR IC l(D BLE Filed Jan. 6, 1934 film ofmznera/ 017.- Jb/.bric

Percy /Wzzgom C/r/ INVENTOR.

ATTORNEY.

Patented Oct. 19, 1937 UNITED STATES 2,096,448 msm'mn ELEcrmc CABLE Percy Morgan Clark, Parlin, N. J., asslgnor to u E. I. du Pont de Nemours Company, Wilmington Del., a corporation ot Delaware Application January 6, 1934, Scrlal No. 705.585

8 Claims.

'I'his invention relates to an improved insulated electric cable, wherein a cellulose derivative composition is utilized as the surface coating, and is a continuation in part of my copending application 5 Serial No. 518,891, filed February 27, 1931.

Electric cables have previously been coated with cellulose derivative compositions thereby providing a finish on the cable which is tough, durable and flexible over a long period of time and which l is highly resistant to various deleterious agents.

These compositions employ a considerable proportion of softener to give a film of the required toughness and flexibility to withstand the rough usage to which cables/y are subjected. A serious l objection to the use of these compositions is that the coatings produce a iilm having a considerable degree of tackiness and thermoplasticity largely due to the relatively high proportion of softener used. This objection has heretofore been par- 20 tially overcome by baking or force drying the coated cable before it is reeled for a prolonged storage period, but this procedure is unsatisfactory as it slows up production, adds to the expense of coating, and does not eliminate the characteristic thermoplasticity of these coatings.

This invention has as an object, the provision of an improved insulated electric cable finished with a coating which is non-tacky and quick drying and which does not require prolonged force 30 drying or cause appreciable delay in reeling the cable subsequent to the coating step. A further object is to provide a cable finished with a coating which, although basically thermoplastic, is protected from tackiness and sticking during prolonged storage. A still further object is the provision of a cable carrying a finish coat which is tough, durable, exible and insulating.

These objects are accomplished by the following invention wherein an insulated electric cable is coated with a cellulose derivative composition which contains a relatively incompatible nonvolatile paraiiin wax free mineral oil, a solvent softener incompatible with the mineral oil, the oil being present vinan amount sufficient to be 45 exuded or spewed out as a thin top film, whereby the tackiness and thermoplasticity which other- Wise would be presentdue to the softener is overcome.

In the drawing,

g `i 'a diagrammatic 50 section of a cabiespro 1 gingtothepresent invention. Figure 2 is also a diagrammatic section of a cable prepared according to the present invention. In both figures, l represents an electrical conductor, 2 is a rubber or other insulating coating, 3 indicates a fabric layer over the 5 said insulating coating, and 4 represents a nlm of lacquer prepared according to the present invention having 'a very thin surface film of exuded mineral oil. The drawing is diagrammatic and the difference is not intended to be drawn to scale.

The composition of the present cable coating comprises a cellulose derivative such as cellulose nitrate, acetate or ether, a solvent softener in sufficient amount to give a lrn of the desired exibility, a non-volatile mineral oil or other nonvolatile oil incompatible with the cellulose derivative in suiiicient amount to be exuded or spewed out and form a thin top film of cil when the coating dries.- The usual lacquer solvents are used in suiiicient quantity to give the composition the desired viscosity, the composition being adapted for use either as a plastic or liquid coat- IDS.

, By the term solvent softener asused herein and in the appended claims is meant those softeners which have an active solvent action on the cellulose derivative constituent of the composition as distinguished from those softeners generally classified as lnon-solvent soitenersV and which do not have an active solvent action on the cellulose derivative, although possibly having some solvent action in the presence of alcohol or other solvents used in some coating compositions.

It is preferable also to use those solvent softeners which are highly incompatible with mineral oil. because it is important to obtain the exudation or spewing out of the mineral oil with the use of as little of this oil as possible, the mineral oil if retained in suiiicient quantity in the dried lrn having a tendency to weaken the film. Tricresyl phosphate, a solvent softener is especially suited for this purpose, due to its extreme incompatibility with mineral oil. Triacetin and benzyl ether are also very incompatible with mineral oil 4r and are also well suited for this purpose. However,:.other solvent softeners such as dibutyl tar- ,tratafciiethyl phthalate, dibutyi phthalate, et cetvera; canbe used satisfactorily.

The' proportion of incompatible oil required to obtain'proper.exudation will depend upon the 50 type of cellulose derivative used and upon the particular softener used. Cellulose nitrate is the preferred cellulose derivative and it has been found that 10 parts by weight of cellulose nitrate with 5-15 parts by weight of softener require between 0.2 to 0.7 part by Weight of mineral oil. It is not desirable to add mineral oil materially above 7% by weight of the cellulose nitrate. It has been found that if this ingredient is added materially above 7% by weight of the cellulose nitrate, for example about 10%, an abnormal and undesirable amount of exudation will frequently result. Thisv causes a decidedly greasy lm which adversely aiects the process of coating the cable and the ultimate i'lnish is likewise not acceptable. When this condition exists the adhesion of the coats applied subsequent to the i'irst is very poor and in some cases in attempting to use such a composition under standard methods of coating is entirely inoperative. When the exudation is excessive the wiper (usually a rubber nipple surrounding the cableI during coating operations) simply wipes off the freshly applied coating because the oily surface of the iirst coating precludes any degree of adhesion for subsequently applied coats. Further, this oiliness is frequently of such magnitude as to present an unsightly appearance and will transfer the oil to anyone handling the cable or to objects or covers coming in contact with it. The rapid accumulation of dust on. the oily surface during storage and in use likewise presents additional adverse factors.

Cellulose acetate is much more incompatible with mineral oil than cellulose nitrate and from 0.1 to 0.5 part by weight of mineral oil to 10 parts of cellulosel acetate form the preferred range. On the other hand, the cellulose ethers are more compatible with mineral oil than cellulose nitrate and 1.5 to 2.5 parts by weight of mineral oil must ordinarily be added to 10 parts of cellulose ether, even though a solvent softener highly incompatible with the mineral oil be used.

Due to the compatibility of cellulose ethers with mineral oil, it is not desirable to use solvent softeners having but slight incompatibility with mineral oil because the proportion of mineral oil that must be added to obtain exudation is so great as to give a materially weakened lm. The solvent softener should be present however in sufficient amount to give the desired exibility and the mineral oil in an amount just sufcient to exude as a thin top layer. It is not necessary that the oily top layer beso thick as to be clearly obvious to the eye, since a thin coat not perceptible to the eye, but suicient to cause a cable coated with the composition to slip when pulled through the fingers, as contrasted to the sticking action of a cable coated with prior art high softener content lacquers, is suilcient to prevent coils of lacquered cable from sticking together even though stored at relatively high temperatures.

' The non-volatile, relatively incompatible oil used in the composition as a coating for cables is preferably a highly purified, non-volatileparain free mineral oil of a viscous nature, such as Nujol, Primol, water white Russian oil,

and high grade lubricating oils, all of which are non-volatile, oily parafiin or naphthene base hydrocarbons.

Resins may for the first time be used satisfactorily in these -highly exible coating compositions and are valuable in increasingthe gloss, b;1i1d,

adhesion and insulating properties of the cable .75- nishand also to decrease inilammability. 'I'he the present purpose, such as natural and treated natural resins and synthetic resins of the polyhydric alcohol-polybasic acid type, with or without modifiers such as drying oils, non-drying oils,

etc., phenolaldehyde type, polymerized vinyl compounds, et cetera, provided that the nished composition has the properties necessary for a commercially practicable product for a coating composition.

As will be understood by those skilled in the art, the cellulose derivative, solvent softener, incompatible oil and, if desired, resin, are dissolved in suitable solvents, such as a mixture of ethyl acetate, ethyl alcohol and toluol, and the resulting solution, with or without coloring matter, llers, et cetera, is applied to the surface of a cable and the solvent allowed to evaporate. If desired, the amount of solvent may be so reduced as to give a plastic composition instead of a lacquer of a viscous composition.

The following examples are the compositions for the cables and not by way of limitation. The parts are by weight:

Example 1.-Clear cable lacquer given. to illustrate.

Nitrocellulose 12.5 Tricresyl phosphate 15.5 Nujo1 00.7 Ethyl acetate 25.0 Denatured alcohol 15.0 Toluol i 31.3

Example 2.-Black cable lacquer Nitrocellulose-, 12.5 Tricresyl phosphate 15.5 Primol 00.7 Ethyl acetate i 24.5 Denaturedl alcohol 15.0 Toluoli 31.3 Nigrosine black (spirit soluble) 00.5 100.0

Example 3.-Cable lac'uer (using a natural resin) Nitrocellulose l l 13.0 Tricresyl phosphate 9.0 Damar resin l 9.0 Water white Russian oil 0.7 Ethyl acetate 22.0 Tnlunl 203 Benzol 16.0 Denatured alf-ohm 10.0

Y 100.0 Example 4.-Cable lacquer (using a synthetic resin) Nitrocellulose 15.0 Tricresyl phosphate 18.0 Synthetic resin; 10.0 Ethyl acetate 25.0 Benzol 24.3 Denatured alcohol 7,0 NUJOI 0.7

CII

The synthetic resin used in this example is a reaction product of:

Per cent Phthailc anhydride 39.3 Glycerine 6.0 Diethylene glycol 21.2 Cocoanut oil 33.5

The resin is prepared by heating the glycerine, diethylene .glycol and cocoanut oil in a closed vessel fitted with a condenser for vabout 3 hours at l480" F. The mixture is cooled slightly and the phthallc anhydride added. The heating is then continued at 450 F. for 2-3 hours or until an acid number of 22 is reached.

Example 5,-Cable lacquer (cellulose acetate) 100.0 Example 7.-Cable lacquer (benzyl cellulose) Benzyl cellulose 12.0 Tricresyl phosphate 6.0 Mineral oil 2.5 Ethyl acetate 15.0 T0luol 54.5 Denatured alcohol 10.0

100.0 Example 8.-Cable plastic Nitrocellulose 27.5 Tricresyl phosphate 37.2 Denatured alcohol 7.1 Mineral oil 0.6 Magnesium carbonate 27.6

These compositions are material improvements over those heretofore known, as the thin oily top layer eliminates the tackiness of the film in a much shorter period of drying and consequently prolonged baking and cooling of coated cables before reeling is not essential. It has been found that twice the speed in passage of the cable through the drying tower is permitted and also that the temperature in the dryigv tower may be reduced. It is possible to put many more coats of lacquer on a cable than previously, without trouble being caused by tackiness of the film. Furthermore, cables coated with this composition may be reeled and stored at relatively high temperatures without sticking together or marring the nish. q

The thin oily fllm on the surface of the nish not only protects it in storage and handling, but adds appreciably to the appearance of the finish, giving a smooth, uniform surface.

The use of an incompatible, non-volatile oil allows the proportion of softener in the composition to be increased without causingtackiness, thereby giving a more flexible finish, a feature particularly desirable in the cable coating art. Also resins may be used in the present compositions in substantial quantities, thereby giving a coating of increased gloss, build, adhesion and insulating properties, and reducing the inflammabllity of the finish. Heretofore the use of resins has been-impractical in compositions designed for coating cable, because of their thermoplasticity.

'I'he herein disclosed invention may be applied to practically any electrical cable. Particularly -good results have been obtained by coating a conventional cablev having a conductor with layers of rubber and fabric with any of the compositions herein disclosed so that the exterior of the coated cable will have a layer of the cellulose derivative composition and exuded therefrom a thin surface film of non-volatile mineral oil.

As many widely different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

Iclaim:

'1. A flexible electric cable coated with a tough, ,durable insulating surface lm comprising a cellulose derivative, solvent softener, and an incompatible non-volatile mineral oil, and having an exuded surface layer of non-volatile mineral oil over said surface film.

2. A flexible electric cable coated with a tough, durable insulating surface film comprising cellulose derivative, solvent softener, a resin, and an incompatible non-volatile mineral oil, and having an exuded surface layer of non-volatile mineral oil over said 111m.

3. A exible ele'ctric cable coated with a tough, durable insulating surface nlm comprising cellu- `lose nitrate, tricresyl phosphate, and an incompatible non-volatile mineral oil, and having a surface layer of non-volatile mineral oil over said nlm.

4. A flexible electric cable coatedlwith a composition comprising 10 parts by weight of cellulose nitrate, 5-15 parts. of tricresyl phosphate, and 0.2 to 0.7 part of an incompatible nonvolatile mineral oil, said composition when free from volatile solvents being tough, durable, insulating, and having a thin surface film of the said mineral oil.

5. A flexible electric cable coated with a tough, durable insulating surface film comprising cellulose nitrate, tricresyl phosphate and from 0.02 to 0.07 part by weight of the cellulose nitrate of an incompatible non-volatile mineral oil and having` 6. A flexible electric cable comprising a rubbery coated metallicv conductor having a. fabric coating over the rubber, said cable having a tough, durable insulating surface coating theren of a composition comprising cellulose nitrate, tricresyl phosphate and from 0.02 to 0.07 part by weight of the cellulose nitrate of an incompatible non-volatile mineral nil and having a thin surface layer of non-volatile mineral oil on, said surface coating. l

7. A flexible electric cable comprising a rubber coated metallic conductor having a fabric coating over the rubber, said cable having a tough, durable insulating surface coating thereon of a composition comprising 100 parts of cellulose nitrate, 50 to 150 parts by weight of tricresyl phosphate and 2 to '7 parts by weight of an incompatible nonvolatile mineral oil and having a thin surface layer of non-volatile mineral oil on said surface coating.

8. An electric cable lacquer having substantialtion having the following formula:

l Per cent Nitrocellulose 12.5 Tricresyl phosphate 15.5 Mineral nil 00.7. Ethyl acetate 25.0 Alcohol Y' 15.0 Toluol 31.3

said properties of the dried ilm including toughness, durability, high insulation, and said dried lm having a thin exuded lm of the mineral oil.

PERCY MORGAN CLARK 

